1. Field of the Invention
This invention relates to tape recorders having tape transport assemblies for driving a recording tape past a record head and between two cartridge reels, and more particularly to such recorders including load survey magnetic tape recorders having both magnetic brake and magnetic clutch arrangements for maintaining controlled and substantially constant tape tensions.
2. Description of the Prior Art
The present invention is closely related and is an improvement of a load survey type of magnetic tape recorder disclosed and claimed in U.S. Pat. No. 3,602,458, assigned to the assignee of this invention. The tape recorder is intended for substantially continuous use in varying environmental conditions requiring highly reliable and rugged construction features. The tape transport assembly of the prior recorder utilizes a mechanical friction producing arrangement for providing a predetermined drag or retarding force on a take-up pulley assembly that receives the supply reel of a removable tape cartridge. The drag maintains a predetermined tension in the recording tape as it is pulled from the supply reel by a capstan assembly of the recorder. The capstan is driven directly from a constant speed drive motor. A take-up pulley assembly engages the take-up reel of the cartridge and is driven by a slipping spring belt which, in turn, is driven by the capstan assembly. Slippage between the spring belt and the take-up pulley assembly occurs to maintain a proper tape speed between the capstan and the take-up reel as the tape is fed thereto. While the aforementioned recorder has been highly reliable and dependable in extended service under sometimes different environmental conditions, reduction of the mechanical and frictional between the retarding and driving coupling of the supply pulley and take-up pulley assemblies is desirable. The associated drag cord and spring belt drive tend to be some limitation to the life of the recorder and require maintenance and cleaning of dirt and debris between the frictional engaging parts. Thus, rotational drag at the supply pulley assembly is desired to be better isolated from a stationary retardation producing member and the driving torque to the take-up pulley assembly is desired to be transmitted across a more maintenance-free clutch interface.
In U.S. Pat. No. 3,636,277, a video tape recorder requires a rotating magnetic head which has a rotation synchronized to the tape speed by a eddy current brake and hysteresis coupling arrangement. Further eddy current brake and hysteresis coupling arrangements are described for the capstan drive and guide rollers. In U.S. Pat. No. 3,967,790, a tape cartridge drive is disclosed having a capstan drive including a magnetic clutch which, in turn, is coupled by gears to a take-up reel spindle. In U.S. Pat. No. 3,809,336, a tape transport is described for bi-directional tape feed and take-up. The transport includes a separate pair of clutches and a separate magnetic coupling, interconnecting each of two tape spools and a drive motor. Symmetrical operation allows the spools to be interchanged as take-up and supply spools operated at high velocities and subject to periodic stopping and starting. An air gap space in each magnetic coupling is exposed to small debris and magnetic particles capable of accumulating thereto to alter the torque and speed characteristics between the input and output of the couplings. U.S. Pat. No. 3,584,250 discloses a film projector take-up reel assembly rather than a tape recorder having a capstan tape drive arrangement. The take-up reel assembly includes a magnetic drive coupling between a drive motor and the take-up reel. A cylindrical cage carries annular permanent magnets and a magnetically permeable ring axially spaced from the permanent magnets. The ring is fixed to a drive shaft of the take-up reel so that the motor torque is transmitted across a magnetic air gap spacing of the coupling. The magnetic coupling air gap is adjustable to adjust the maximum load transmitted by the coupling. Upon film rewinding, the magnetic gap coupling provides magnetic breaking as film is fed off of the take-up spool.
The present invention is directed to an improved tape drive arrangement for a unidirectional slow speed and continuously operating magnetic tape recorder having a magnetic brake at a supply spindle assembly and a magnetic clutch at the take-up spindle assembly to provide reliable and consistent operation, and for controlling the supply and take-up tape tensions and speeds wherein the magnetic clutch and brake arrangements include relatively movable parts including a magnetized part and a permeable magnetic part separated by a protected non-magnetic gap space to prevent undesired accumulations of foreign material altering desired relative rotation between the two magnetic coupling parts.